S. I. Smith 071 American Crustacea. 127 



du jNIuseum, differ so much that it would scarcely be supposed that 

 they were intended to represent the same species, much less the same 

 specimen. 



The only generic characters which are given by Edwards to distin- 

 guish Adinthoplax from Gehtsinius, the proportions of the carapax 

 and the tuberculation of the branchial regions, appear to me to be of 

 slight importance. In the proportions of the carapax, the difference 

 between Acanthoplax as figured in the Aunales des Sciences and the 

 ordinary narrow fronted Gelasimi is scarcely, if any, greater than the 

 difference between the two figures of A. inslgnis, for the figure of the 

 carapax in the Annales is 19-0'"'" in length and 27'5'"'" in breadth, giv- 

 ing tlie ratio of length to breadth, 1 : 1 '45, while the carapax in the 

 figure in the Archives du Museum is 25-2™'" in length and 32-0"'"' in 

 breadth, giving the ratio, 1 : r27, and this when both figures are 

 stated to be of natural size. No measurements are given in the text 

 in either place. The tuberculation of the branchial regions appears 

 to be merely a character of ornamentation to which there is a consid- 

 erable approach in the females of many of the large Gelasimi, and in 

 the male G. armatus described in this article, there is a still closer 

 approach to it. 



The armature of the ambulatory legs, however, may prove to be a 

 character of some importance, and would unite in one group with A. 

 insignis, G. ornatus and G. arinatus, and perhaps also G. niaracoani. 



B. — Species in ivliich all the segments of the abdomen are separated by distinct articula- 

 tions, hut in luhich the front is broad and evenly arcuate between the bases of the ocular 

 peduncles. 



Gelasimus palustris Edwards. 



(?) Cancer vocator Herbst, op. cit., Band iii, viertes Heft, p. 1, Tab. 59, fig. 1, 1804. 



Gelasimus vocans Edwards, Histoire naturelle des Crust., tome ii, p. 54; et Eegne an- 

 imal de Cuvier, 3™^ edit, Crust., pi. 18, fig. 1 (teste Edwards). 



Gelasimus pahMtris Edwards, Annales des Sciences naturelles, 3™e gerie, Zooloo-ie 

 tome xviii, 1852, p. 148, pi. 4, fig. 13. 



[Xon Cancer vocans Linne, Systema Naturae, editio xii, tome i, p. 1041). 



As figured in the Annales des Sciences naturelles, this species is 

 quite different from any species which I have examined, and is distin- 

 guished by the form of the terminal segment of the male abdomen 

 which is as long as its breadth at base, with the sides straight and 

 slightly divergent and the extremity broad and rounded, and by the 

 anterior margin of the orbital border being symmetrical and not more 

 rapidly curved above the base of the ocular peduncle than on the out- 

 side, as it is in most of the allied species. It is described in the fol- 



